The present invention relates to arthodesis for stabilizing the spine. More specifically, the present invention is directed to an intervertebral spacer formed of a bone material and to methods of treating patients having spinal deformities.
Removal of damaged or diseased discs and restoration of disc space height to treat chronic back pain and other ailments are known medical techniques. Implants such as intervertebral spacers are often implanted in the disc space to maintain or reestablish disc space height after removal of all or a portion of the disc. The spacers can be formed of a variety of both resorbable and non-resorbable materials, including, for example, titanium, surgical steel, polymers, composites, and bone. It is also often desirable to promote fusion between the vertebral bodies that are adjacent to the damaged or diseased discs. Typically an osteogenic material is combined with a spacer and inserted in the disc space to facilitate and promote bone growth. While the selection of the implant configuration and composition can depend upon a variety of considerations, for arthodesis it is often desirable to select a resorbable material than does not stress shield the bone ingrowth. Bone and bone-derived components can provide suitable material to prepare the implants. However, bone material acceptable for use in implants is a scarce resource, being derived from limited human tissue donor resources.
Suitable bone or bone-derived material for use in implants, in general, is almost exclusively obtained from allograft and xenograft sources, both which are precious resources. Since intervertebral spacers must withstand the compressive loads exerted by the spine, these implants are often formed from cortical long bones, which are primarily found in the lower limbs and include, for example, femur, fibula, and the tibia bones. The long bones makeup only a fraction of the available bone source. Thus, sources of bone suitable for structural intervertebral spacers are extremely limited. The scarcity of desired donor bone makes it difficult to provide implants having the desired size and configuration for implantation between adjacent lumbar vertebrae, which can require relatively large implants. It is further anticipated that as the population ages there will be an increased need for correction for spinal deformities and a concomitant increase in the demand for bone-derived components. Therefore, these structural bone portions must be conserved and used efficiently to provide implants. The scarcity of suitable bone material has also hindered efforts to design and manufacture varying configurations of suitable implants for arthodesis of the spine. Further, various implant configurations have not been physiologically possible to obtain given the structural and geometrical constraints of available donor bone.
In light of the above-described problems, there continues to be a need to provide suitable implants to facilitate patient treatment. The present invention addresses this need and provides a variety of other benefits and advantages.
The present invention relates to spinal implants, the manufacture and use thereof. Various aspects of the invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms and features, which are characteristic of the preferred embodiments disclosed herein, are described briefly as follows.
In one form, the invention provides an implant for promoting bone fusion between adjacent vertebral bodies. The implant has a longitudinal axis and comprises an assembly of cortical bone-derived components. The components are comprised of a first strut having a first bone-engaging portion and an opposite second bone-engaging portion. A first impact surface is disposed between the first bone-engaging portion and the second bone-engaging portions. The bone-derived components also include a second strut spaced from the first strut. The second strut has a third bone-engaging portion and an opposite fourth bone-engaging portion. A second impact surface is disposed between the third and fourth bone-engaging portions. The components also include an elongate cross-member that extends from the first strut to the second strut. The second strut in cooperation with the first strut defines an internal space. In one embodiment the implant can be provided as an open cage. An osteogenic material can be combined with the implant. The osteogenic material can be interposed between the first and second strut. Preferably, the osteogenic material is provided to be formed within the internal space and/or adherent to at least one of a first strut, the second strut, and the cross-member. The osteogenic material can also be adapted to be moldable to provide a semi-rigid shaped component.
In alternative forms, the first and second strut can be defined by substantially planar walls that can be adapted to restore normal disc height and/or provide correct lordosis of the spine. The first and second strut can include opposite bone-engaging portions that are separated from each other at a first end of the strut by a distance D1 and wherein the opposite bone-engaging uniformly taper to a second distance D2 at a second end of the strut, such that D1 is greater than D2. Alternatively, the bone-engaging portions can define an arcuate surface wherein the opposite bone engaging portions separate from each other at a maximum distance at a point located between the first and the second end on the respective strut. In still yet other embodiments, the first and second struts can define curved wall portions that approximate the medullary canal of a long bone.
In another form, the present invention provides an implant for promoting bone fusion. The implant has a longitudinal axis and comprises an assembly of cortical bone-derived components. The components comprise a first strut having a first bone-engaging portion and an opposite second bone-engaging portion. The first strut also includes a first slot formed therein and extending from the first bone-engaging portion. The first slot has a first internal wall portion and opposing second internal wall portion and an internal end wall portion therebetween. The implant assembly also comprises a second strut that has a third bone-engaging portion and an opposite fourth bone-engaging portion. The second strut also has a second slot formed therein and extending from the third bone-engaging portion. The second slot includes a first internal wall portion and opposing second internal wall portion and internal end wall portion therebetween. The first slot is adapted to receive a portion of the second strut, and the second slot on the second strut is adapted to receive a portion of the first strut to interengage the first and second strut to form the implant assembly. When thus configured, the implant can be adapted to be inserted in the intervertebral space or, alternatively, the implant can be sized to provide a replacement for a vertebral body.
The present invention also provides a method of treating a spinal deformity. The method comprises surgically preparing a intervertebral space between adjacent endplates of adjacent vertebrae and inserting an implant into the prepared space. The implant comprises a first strut having a first bone-engaging portion, an opposite second bone-engaging portion and a first impact surface disposed therebetween, a second strut spaced from said first strut, said second strut having a third bone-engaging portion, an opposite fourth bone-engaging portion, and a second impact surface disposed therebetween, said second strut in cooperation with said first strut defining an internal space, and a cross-member extending from the first strut to the second strut into the intervertebral space.
In yet another form the present invention provides other methods for treating spinal deformities. These methods include surgically preparing a patient to receive a spinal implant; and implanting an implant comprising of an assembly of cortical bone-derived components. The cortical bone-derived components include: a first strut having a first bone-engaging portion and a opposite second bone-engaging portion, said first strut having first slot formed therein, and a second strut having a third bone-engaging portion and a opposite fourth bone-engaging portion, said second strut interengaging said first strut to form the implant.
Further objects, features, aspects, forms, advantages and benefits shall become apparent from the description and drawings contained herein.